Amiga500
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 7:41 pm

XRAYretired wrote:
Can a I suggest an exercise bike set up in 1st class galley with a heavy duty fan belt wrapped around the trim wheel.


I was thinking more attach a big balloon to the tailplane and have pipes picking up from 1st class - with valves controlled from flight deck.


That constant never ending supply of hot air from the sh...e being spewed would blow the balloon up and pitch that nose down in no time.
 
rj777
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 7:48 pm

Don't know if anybody's heared about this, but UA is putting 777s and 787s on Max Routes:
https://www.paddleyourownkanoo.com/2019 ... grounding/
 
planecane
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 8:27 pm

zeke wrote:
XRAYretired wrote:
Its not my solution, I'm just interpreting the description given by Boeing. However, It has been reported in these threads that a pilot may not experience the condition that would MCAS operation but once in his carreer, if so, then MCAS being needed and not available is likely to be in the extremely remote likelyhood range.

Ray


I don’t understand the implementation. My understanding is MCAS is designed to deal with a high speed dynamic stall like in a spiral dive.

I do not understand why it is necessary to change the stab trim, I would have thought if it was a linear control force for deflection they are trying to achieve the more sensible approach would be via the elevator feel computer to change the control column feel without changing the aerodynamics.


My guess would be that the elevator feel computer doesn't have AoA as a possible input and only changes feel based on speed. Since the situation that required MCAS involves AoA it couldn't be done by the elevator feel computer without redesigning it. Just a guess based on no actual information.
 
XRAYretired
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 8:41 pm

planecane wrote:
xmp125a wrote:
planecane wrote:
I'm assuuming this is the reason that the software change involves more than just response to sensor values. By limiting the total authority to 2.5 degrees per event and only activating once per event, it mitigates the issue of simultaneous AoA sensor failures because the worst case would be recoverable.


But again. If there WAS a good reason to extend thre authority of MCAS, such hack should be provided. Or we will talk in one year how one of them "3rd world pilots" without difference sim training crashed another MAX by inadvertenly stalling it! That approach is horrible! Wherever I saw such approach I knew it would not work and indeed it is good just for some lab demos where you need to show someone "it does work now within the deadline". And it is deeply flawed and immoral to put something like that in production.


There was a good reason to extend the authority of MCAS from 0.6 degrees to 2.5 degrees. There was no intention for it to trim down more than 2.5 degrees in normal operation. It was the poorly thought out fault tree analysis that led to the full nose down authority.

Just to get the numbers right. The original design ran at 0.25 deg/sec, and the revised design 0.6 deg/sec. In both cases, the system was designed to abort when the AOA actual fell below the trigger value. It is in fault condition that MCAS will continue to drive AND since AOA actual may never dip below the trigger value

Ray.
 
RossW
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 8:51 pm

A good video for the average Joe

https://youtu.be/H2tuKiiznsY
 
hivue
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:07 pm

planecane wrote:
By limiting the total authority to 2.5 degrees per event and only activating once per event, it mitigates the issue of simultaneous AoA sensor failures because the worst case would be recoverable.


Are you sure? With 2.5 deg of stabilizer AND (half the total available) at Vmo with the stab trim cutout switches flipped so no manual electric trim close to the ground it might not be a recoverable situation. Boeing needs to be very carful how they do this.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
MSPNWA
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:08 pm

RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


If the Average Joe wishes to be misinformed, yes, it's a good video.
 
IWMBH
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:10 pm

MSPNWA wrote:
RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


If the Average Joe wishes to be misinformed, yes, it's a good video.


What is wrong in the video?
 
ArgentoSystems
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:42 pm

I did not find any misinformation.
 
kalvado
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:55 pm

IWMBH wrote:
MSPNWA wrote:
RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


If the Average Joe wishes to be misinformed, yes, it's a good video.


What is wrong in the video?

It doesn't fully exonerate Boeing. And such approach is totally unacceptable. At least to some people.
Video should focus on the fact that third world junky airlines crashed MAX, while US operators didn't have a single accident.
 
hivue
Posts: 1957
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 9:58 pm

[*]
ArgentoSystems wrote:
I did not find any misinformation.


You would find no misinformation in an empty book either.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
Paolo18
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 10:02 pm

Boeing's panacea is not merely a software fix but moreso a faa fix.
 
skyharborshome
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 10:33 pm

kalvado wrote:
IWMBH wrote:
MSPNWA wrote:

If the Average Joe wishes to be misinformed, yes, it's a good video.


What is wrong in the video?

It doesn't fully exonerate Boeing. And such approach is totally unacceptable. At least to some people.
Video should focus on the fact that third world junky airlines crashed MAX, while US operators didn't have a single accident.


To people who feel that way, I would ask how many times do we have to go over this? Any human life lost is the same no matter where they live and no matter what nationality is on the side of the plane. Boeing's job is to produce a product that is safe and reliable. If the plane was 100% safe and reliable then we would not be in this situation. Furthermore, we will never know what would have happened if the fleet was not grounded worldwide. Do American citizens on American soil flown by American pilots on American-based airlines must die for us to go...."hmmm... I guess it was the plane." The answer is no. I do not care what arguments to the contrary are, the answer is no.
Fly CHD!
 
kayik
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 10:50 pm

Oykie wrote:
According to ATW FAA targets late May, early June re authorization for the 737MAX.

http://m.atwonline.com/regulation/faa-t ... s-approval


One thing I don't understand. Why FAA is targeting something related to MAX? Is this within their job description? It is hard to believe that this was an FAA statement and they are doing their best to lose their credibility by 100%. Let Boeing target for delivering results to FAA and others.
 
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ACCS300
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 10:51 pm

RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


Yes, brilliant account and production, I've forwarded this to a few friends and colleagues who've not quite been able to grasp what's transpired.

Lives matter, those responsible must be held fully accountable, this is a dark story of greed and deceit, sad, sad days for Boeing and a wake-up call to the aviation industry. I hope good comes of this and we return to proper process for certifying aircraft that fly our loved ones.
 
StarAC17
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 11:07 pm

IWMBH wrote:
bennett123 wrote:
https://www.bbc.co.uk/news/world-us-Canada-47928356

Following confirmation from AA that they will be grounding their MAX’s until Mid August how much spare capacity do they have?.

Thinking more widely, how much scope is there for carriers to just hang on with existing equipment.

I know that ACMI operators exist, but that is not cheap and I doubt that they have a huge amount of free capacity especially coming into the Summer.


I think AA can handle the grounding of their MAX fleet, the MAX order where partly meant to replace -800's. They just hang on to them a little longer.
Carriers like AC and FI are in bigger trouble because it involves a much larger percentage of their fleet.


IIRC the grounding of the max is affecting 2% of AC's operations. They can do some creative fleet management and the max is there to replace older A320's.

xmp125a wrote:
Turnhouse1 wrote:
Oykie wrote:
According to ATW FAA targets late May, early June re authorization for the 737MAX.

http://m.atwonline.com/regulation/faa-t ... s-approval


Are the CAA or EASA likely to take the FAA at their word, or will Boeing need to do full applications in each country/region? If so it could be a lot longer before the ban is lifted outside the USA.


Boeing needs to be accepted in every country, this has not changed. However, in the past, all, even the big agencies (e.g. EU's EASA) followed FAA's lead and the small countries really have no leverage if they don't want for international travel to avoid them.

What has changed is that now EASA will not blindly accept FAA's certification. Since no one wants to do same work twice, I am pretty sure that FAA and EASA will find a way to re-establish trust, but this means MAX will be under really heavy scrutiny until both agencies (and some more, e.g. Chinese) is satisfied. That certainly means that the grounding will be perhaps longer than shorter.

These things are now crystal clear to FAA and Boeing as well, as they already started assembling truly international investigation board https://www.airlineratings.com/news/maj ... g-737-max/

(Which is actually the good news for Boeing and the travelers, as one can be sure that if the board decides that ban should be lifted, it will be based on others, not only FAA)


Correct and if that trust is not rebuilt expect that these agencies will not let the 777X fly with the FAA approval solely.

Incidents like this are why regulations are stringent and people have short memories as to why they are needed. Most regulations be it airline safety ones, two in the cockpit, getting everyone off in 90 seconds, rest times etc. stem from mistakes or incidents that when investigated reveal a flaw.
Other regulations like banking regulations, building codes etc. are in place because something went wrong and it was investigated and the regulations were then suggested.

jagraham wrote:
Revelation wrote:
astuteman wrote:
The cultural balance (the "ethic") within Boeing management is very demonstrably not right just now, and it needs to change.
In this country, the TA, Chief Engineer, Programme Head and CEO would all be on gardening leave or would have left by now, pending criminal proceedings.

Accountability. And Ethical leadership...…….
I will be fascinated to see how this one turns out.

As a fish swimming in the ocean of US cultural norms over the last several decades, I think I'd use the word depressing rather than fascinating to describe how things will turn out. We follow the golden rule here these days: he who has the gold rules. Ethical concerns are a quaint reminder of days long gone. From what I've seen of UK culture (I have relatives there and visit every few years) your culture is converging towards ours at a fast pace. I'm glad you still have a pond to swim in where ethics still matter.

Personally I think management used to understand why ethics mattered, precisely because if business wasn't conducted with pristine ethics you could end up in situations like this MAX one (if we believe the way the media is reporting the situation) or something like Dieselgate. Now it seems management is indoctrinated in the rulers versus the ruled value system, and listening to one of 'their' complaints about ethics is akin to giving away management's power to control all events. I found myself working through a weeks long ethical bind at my last place of employment. I had drawn a line in the sand where I would not approve certain statements akin to the ones in your industry. Management found a weasel way to work around that, they just found one of my peers who was more focused on career growth rather than ethics, and he signed off willingly. Point being, I think management views ethical concerns as asymmetric warfare: Why should we give the peons the equivalent of IEDs (improvised explosive devices) that can blow up our project? Best to manage our way around such things, no?

astuteman wrote:
For what its worth, I'm pretty sure the MAX will fly again this year and continue on its journey.
But I think its lifetime is limited now, moreso than it was before

It's hard to argue that point. Thanks as usual for your thoughtful post. I hope it doesn't go unnoticed amongst all the people trying to display their mathematical superiority over others. I feel like I'm reading "stats for dummies" rather than airliners.net! :-)



Engineer draws line in sand. Managers find another engineer to sign off. Challenger disaster.
It's important for the managers to understand the engineering.
It's vitally important for the top execs to either trust the managers or do the management themselves.
Signature shopping is not good . .


Ahh the old if mom won't let me do it I will ask dad.

I don't know if there are any American licensed professional engineers that can weigh in. I studied engineering in University but did not get my professional designation because I switched careers, in Canada engineers are licensed with public safety as #1 and has the obligation to not sign off an unsafe design. I would assume this is the same in the United States for professional engineers.

Unforeseen negligence is not an excuse and Boeing realizing that the pitch up made this happen should have either redesigned the landing gear to lift the plane up or had training for MCAS.

bennett123 wrote:
IMO, for Boeing/FAA to try to railroad the rest of the world into flying an unsafe aircraft would be a disaster. How long before another ‘safe’ B737MAX goes down with all hands.

Boeing needs to get this right.


They realize this now and are acting on it. Which is why the plane is going to be grounded for what looks like six months.
Engineers Rule The World!!!!!
 
morrisond
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 11:10 pm

ArgentoSystems wrote:
morrisond wrote:
Totally not right - the MAX would be fine without MCAS - it is stable - MCAS just keeps the controls from feeling too light at High Angle's of Attack which would make it easier for a Pilot to pull it into a stall - if they ignore the Stick Shaker, the audio warnings and the frame buffeting - making it extremely unlikely even the worst pilots in the world would put it in stall.

You make it sound like MCAS is completely redundant. You understand that that it simply impossible?


Or overregulation that doesn't really do anything to improve safety in any meaningful manner. However it was a regulation that Boeing had to meet and unfortunately it seems Boeing put about as much effort into it as it would to improve safety.
 
StarAC17
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 11:50 pm

SEU wrote:
Question for those more knowledgeable, are there any other mainstream planes that need a computer to maintain flight stability or is it just the MAX? Because my understanding this plane needs it because of the positioning of the Engines makes it unstable during climb?

My worry here is that the plane might not be allowed to fly again if this is not a normal thing. Boeing can and will fix the MCAS /software issues, but will authorities around the world allow a plane that needs a computer to maintain stability or will they decide thats too far?


It has the tendency to pitch up in a high angle of attack, sounds good in theory.

- However systems like this work much better in FBW systems where the computer is manipulating pilot inputs to the fight controls and the max in not FBW.
- FBW systems IIRC allow for systems that are going haywire to be disconnected and the only computer function would be manually and you would not have to fight with mechanical trim wheels.
- It relied on one angle of attack sensor and made the option of 2 and the mismatch system an extra which is nickel and dime-ing by Boeing.
- In systems like this it should have 3 sensors so if one fails and the other two are consistent then the systems can respond to that. Two is better than one but the odds of 2/3 failing is far less that 1/2 failing and there should be an easy disconnect for MCAS, like hitting an MCAS cancel button.

Granted their will more than likely be checklist improvements such as engaging flaps or some other way of getting MCAS disabled easily.
It looks like their is some pilot error here but that error is almost expected considering that they could not get level flying and forgot to pull the throttle back. It looks like most accidents where many things happened all at once that led to the accident.

skyharborshome wrote:
kalvado wrote:
IWMBH wrote:

What is wrong in the video?

It doesn't fully exonerate Boeing. And such approach is totally unacceptable. At least to some people.
Video should focus on the fact that third world junky airlines crashed MAX, while US operators didn't have a single accident.


To people who feel that way, I would ask how many times do we have to go over this? Any human life lost is the same no matter where they live and no matter what nationality is on the side of the plane. Boeing's job is to produce a product that is safe and reliable. If the plane was 100% safe and reliable then we would not be in this situation. Furthermore, we will never know what would have happened if the fleet was not grounded worldwide. Do American citizens on American soil flown by American pilots on American-based airlines must die for us to go...."hmmm... I guess it was the plane." The answer is no. I do not care what arguments to the contrary are, the answer is no.


Many US pilots reported the plane's flight characteristics as different and noticed MCAS in flight.
The reports that pilots in the US had concerns means that perhaps there has been unreported close calls
Engineers Rule The World!!!!!
 
MSPNWA
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Re: B737MAX Grounded Worldwide

Mon Apr 15, 2019 11:50 pm

IWMBH wrote:
What is wrong in the video?


I saw an interesting preview graphic and jumped in at the 3 minute mark. I was immediately and continuously given inaccurate information before I turned it off. It's a disturbingly bad video that unfortunately will misinform the public further. It's not a question of what's wrong with the video, it's a question of what's right. In that one minute, I can't name one thing that is accurate, fairly represented, and relevant.
 
jagraham
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 1:32 am

speedbored wrote:
jagraham wrote:
The 737 MAX will fly when it is safe. With a political delay.

Why would you expect a political delay? Seems to me that any advantage that could possibly be gained from this grounding by Boeing's competitors would be far outweighed by the damage caused to airlines from having parts of their fleets grounded, added to a whole lot of inconvenience for many of the traveling public.


When bureaucrats embarrass their departments, they can get fired. In addition, the FAA has a reputation to uphold. So it will NOT be business as usual regarding the MCAS fix
 
jagraham
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 1:35 am

A mechanical system can do what FBW does, but it's usually heavier.
Besides the 737 MAX is partially FBW (ailerons, not tailplane)
https://www.intelligent-aerospace.com/a ... ments.html
 
MUWarriors
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 1:45 am

MSPNWA wrote:
IWMBH wrote:
What is wrong in the video?


I saw an interesting preview graphic and jumped in at the 3 minute mark. I was immediately and continuously given inaccurate information before I turned it off. It's a disturbingly bad video that unfortunately will misinform the public further. It's not a question of what's wrong with the video, it's a question of what's right. In that one minute, I can't name one thing that is accurate, fairly represented, and relevant.

With so many inaccuracies you should be able to cite like 4-5 of them, and prove how they're inaccurate with reliable sources. I'm excited to see what you have.
 
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SheikhDjibouti
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 2:21 am

XRAYretired wrote:
planecane wrote:
There was a good reason to extend the authority of MCAS from 0.6 degrees to 2.5 degrees. There was no intention for it to trim down more than 2.5 degrees in normal operation. It was the poorly thought out fault tree analysis that led to the full nose down authority.

Just to get the numbers right. The original design ran at 0.25 deg/sec, and the revised design 0.6 deg/sec. In both cases, the system was designed to abort when the AOA actual fell below the trigger value. It is in fault condition that MCAS will continue to drive AND since AOA actual may never dip below the trigger value

Ray.

I'm taking the risk that I have remembered this wrong, but regarding getting the numbers right, I'm backing planecane.
The original specification was for 0.6degrees in total.
The revised specification as seen on current MAX's, is 2.5 degrees in total, operating at 0.27deg/sec for 9.2 seconds.

(FWIW this 9.2 seconds was rounded up to "10 seconds" in FCOM Bulletin TBC-19 and EAD 2018-23-51)

However, when it comes to "there was no intention for MCAS to trim down more than 2.5degrees", I do not recall seeing this claim made anywhere else on these forums
Planecane - have you got a source?
In normal operation, why would Boeing want to limit it to a single iteration?
Nothing to see here; move along please.
 
planecane
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:07 am

SheikhDjibouti wrote:
XRAYretired wrote:
planecane wrote:
There was a good reason to extend the authority of MCAS from 0.6 degrees to 2.5 degrees. There was no intention for it to trim down more than 2.5 degrees in normal operation. It was the poorly thought out fault tree analysis that led to the full nose down authority.

Just to get the numbers right. The original design ran at 0.25 deg/sec, and the revised design 0.6 deg/sec. In both cases, the system was designed to abort when the AOA actual fell below the trigger value. It is in fault condition that MCAS will continue to drive AND since AOA actual may never dip below the trigger value

Ray.

I'm taking the risk that I have remembered this wrong, but regarding getting the numbers right, I'm backing planecane.
The original specification was for 0.6degrees in total.
The revised specification as seen on current MAX's, is 2.5 degrees in total, operating at 0.27deg/sec for 9.2 seconds.

(FWIW this 9.2 seconds was rounded up to "10 seconds" in FCOM Bulletin TBC-19 and EAD 2018-23-51)

However, when it comes to "there was no intention for MCAS to trim down more than 2.5degrees", I do not recall seeing this claim made anywhere else on these forums
Planecane - have you got a source?
In normal operation, why would Boeing want to limit it to a single iteration?

I'll try to dig up the article but one of the news articles described that test pilots determined that 2.5 degrees was necessary in some cases to offset the nacelle induced lift. The way it was described indicated that 2.5 degrees would be the max needed. Also the fact that the software update will limit it to one activation per near stall event indicates that for the intended purpose only one activation and a total of 2.5 degrees is all that is necessary.
 
RawSushi
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:12 am

RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


Good for the most part, but they got it wrong when they said the pitch up moment was due to thrust from the more powerful engines. That's not the reason for MCAS. The reason for MCAS is the rotational moment caused by having a larger flat-bottomed nacelle further forward of the CG of the plane.
 
RawSushi
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:16 am

ArgentoSystems wrote:
morrisond wrote:
Totally not right - the MAX would be fine without MCAS - it is stable - MCAS just keeps the controls from feeling too light at High Angle's of Attack which would make it easier for a Pilot to pull it into a stall - if they ignore the Stick Shaker, the audio warnings and the frame buffeting - making it extremely unlikely even the worst pilots in the world would put it in stall.

You make it sound like MCAS is completely redundant. You understand that that it simply impossible?


MCAS is redundant from a safety point of view. They only added it to ensure common handling characteristics between the NG and the MAX so that airlines don't have to pay for simulator time to certify pilots for the MAX.
 
planecane
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:17 am

hivue wrote:
planecane wrote:
By limiting the total authority to 2.5 degrees per event and only activating once per event, it mitigates the issue of simultaneous AoA sensor failures because the worst case would be recoverable.


Are you sure? With 2.5 deg of stabilizer AND (half the total available) at Vmo with the stab trim cutout switches flipped so no manual electric trim close to the ground it might not be a recoverable situation. Boeing needs to be very carful how they do this.

Electric trim would be there. The recovery procedure is to balance the control forces with manual electric trim BEFORE moving the switches to cutout.

Also, as thousands of 737s have flown tens of millions of fights for 50 years, statistics should be available for the number of dual AoA sensor failures.
 
RawSushi
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:18 am

planecane wrote:
I'll try to dig up the article but one of the news articles described that test pilots determined that 2.5 degrees was necessary in some cases to offset the nacelle induced lift. The way it was described indicated that 2.5 degrees would be the max needed. Also the fact that the software update will limit it to one activation per near stall event indicates that for the intended purpose only one activation and a total of 2.5 degrees is all that is necessary.


First of all 2.5 degrees regardless of airspeed sounds dangerous to me and maybe some experts can try and explain how that can even remotely be a good idea.

Secondly I think it's telling that the update limits it to one activation only. This means that using AoA to close the loop was never required in the first place and the original design was massively flawed.
 
planecane
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:29 am

RawSushi wrote:
planecane wrote:
I'll try to dig up the article but one of the news articles described that test pilots determined that 2.5 degrees was necessary in some cases to offset the nacelle induced lift. The way it was described indicated that 2.5 degrees would be the max needed. Also the fact that the software update will limit it to one activation per near stall event indicates that for the intended purpose only one activation and a total of 2.5 degrees is all that is necessary.


First of all 2.5 degrees regardless of airspeed sounds dangerous to me and maybe some experts can try and explain how that can even remotely be a good idea.

Secondly I think it's telling that the update limits it to one activation only. This means that using AoA to close the loop was never required in the first place and the original design was massively flawed.


It isn't 2.5 degrees regardless of airspeed. The algorithm uses AoA and airspeed to determine the nose down trim amount. The reason it went to max with the failed sensor is that the AoA was reading so nose high that if it was real the plane would stall at any speed.

100% agree with your second statement. MCAS might be the worst algorithm I've ever seen for a control system. Not just in aircraft. A cell phone charger algorithm has more intelligence.
 
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zeke
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:35 am

IWMBH wrote:
What is wrong in the video?


MCAS is not designed to work low speed after takeoff like suggested in the video, it is designed to operate at high speed when the flaps are retracted like in a high speed spiral dive.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
Virtual737
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:38 am

MD80Ttail wrote:
Zero chance of this happening. The Max will fly again and be totally safe. The rest of the world won’t dare block the Max if the FAA reinstates it’s AW cert withdrawing the grounding. There will be plenty of hyperbole, chest pumping and positioning but at the end of the day will amount to nothing more than fodder for the news media.

On the face of it the MCAS issue will be solved and the plane will be safe. Period. On the backside politics if needed will come into play. Even China will pipe down if they want to keep sending their junk to the US without huge tariffs and if they want to avoid issues in the South China Sea.

Boeing is integral to our economy and national defense and rightly so.


It sounds like we've come full circle and achieved nothing then. Isn't this attitude of "we say it is good and that's all you need to know" a strong factor of why we're here in the first place? Add to that the "toe the line or we'll up the tariffs and see you near the Philippines" and it wont be long until we're here all over again.

What really scares me is that you're probably right.
 
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zeke
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 3:40 am

planecane wrote:
My guess would be that the elevator feel computer doesn't have AoA as a possible input and only changes feel based on speed. Since the situation that required MCAS involves AoA it couldn't be done by the elevator feel computer without redesigning it. Just a guess based on no actual information.


They did resign the FCC from what I can figure out they moved the SYMD from being its own box into the FCC as a software application (SYMD no longer its own item in the MEL). Could have had the elevator feel computer brought inside the FCC as well as a software application.
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FluidFlow
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 6:55 am

I have a feeling Boeing does not tell the whole truth about MCAS at what it is supposed to do. While I think its not there to prevent a stall in situations where the pilots give nose up commands in straight flight, its for situations where the plane turns probably at high speed small turning circle situations. In straight flight stick shaker and other warnings help enough.
Looking at the engine placement i have a feeling that in turns with high bank angles and high AoA the outer wing might stall way before stick shaker will activate. I also think MCAS kicks in way before stall warnings occur.
The reason i think this could be the reason for MCAS implementation is that the nacelle of the outer wing in a turn deflects the flow towards the inner part of the wing where most of the lift is normally generated. This probably happens rather sudden at a certain AoA that on the NG is no problem. Thats also why MCAS was upped from the low value of 0.6 degree to the 2.5 as the nose down has to happen fast in that situation. It must be a pretty aprupt change from a AoA needed for a sharp turn into an AoA that stalls the outer wing. The fact that test flights shown that MCAS planned to „weak“ first suggest Boeing knew in which situation it is needed from simulations and told test pilots to go into such turns to test the limits and figured MCAS needs stronger reaction to prevent a stall as it comes sudden and way before the normal stall warnings.
 
Tristarsteve
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 7:28 am

zeke wrote:
planecane wrote:
My guess would be that the elevator feel computer doesn't have AoA as a possible input and only changes feel based on speed. Since the situation that required MCAS involves AoA it couldn't be done by the elevator feel computer without redesigning it. Just a guess based on no actual information.


They did resign the FCC from what I can figure out they moved the SYMD from being its own box into the FCC as a software application (SYMD no longer its own item in the MEL). Could have had the elevator feel computer brought inside the FCC as well as a software application.


I have no knowledge of the MAX., but the elevator feel computor on all the older B737s was not an electronic computor. It had inputs from two separate pitot heads on the fin, and from stab position and was full of hydraulics. It put a load into the elevator control system. There is no wiring or electronics in it.
I suspect the MAX is the same.
 
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zeke
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 7:41 am

Tristarsteve wrote:
I have no knowledge of the MAX., but the elevator feel computor on all the older B737s was not an electronic computor. It had inputs from two separate pitot heads on the fin, and from stab position and was full of hydraulics. It put a load into the elevator control system. There is no wiring or electronics in it.
I suspect the MAX is the same.


You are very correct. I should be more precise. I was thinking along the lines of how they already use the elevator shift feel module to increase the control column pressure through the elevator feel computer. My understanding is this is driven by the SYMD which I think is just part of the FCC on the MAX unlike previous variants, I have not been able to confirm this.
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WIederling
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 7:56 am

zeke wrote:
I would suggest a fair proportion of the in service failures come from external factors like ramp damage, bird sirikes etc.


But that does not reflect into MTBF numbers. MTBF is an intrinsic property.
Murphy is an optimist
 
XRAYretired
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 8:07 am

SheikhDjibouti wrote:
XRAYretired wrote:
planecane wrote:
There was a good reason to extend the authority of MCAS from 0.6 degrees to 2.5 degrees. There was no intention for it to trim down more than 2.5 degrees in normal operation. It was the poorly thought out fault tree analysis that led to the full nose down authority.

Just to get the numbers right. The original design ran at 0.25 deg/sec, and the revised design 0.6 deg/sec. In both cases, the system was designed to abort when the AOA actual fell below the trigger value. It is in fault condition that MCAS will continue to drive AND since AOA actual may never dip below the trigger value

Ray.

I'm taking the risk that I have remembered this wrong, but regarding getting the numbers right, I'm backing planecane.
The original specification was for 0.6degrees in total.
The revised specification as seen on current MAX's, is 2.5 degrees in total, operating at 0.27deg/sec for 9.2 seconds.

(FWIW this 9.2 seconds was rounded up to "10 seconds" in FCOM Bulletin TBC-19 and EAD 2018-23-51)

However, when it comes to "there was no intention for MCAS to trim down more than 2.5degrees", I do not recall seeing this claim made anywhere else on these forums
Planecane - have you got a source?
In normal operation, why would Boeing want to limit it to a single iteration?


Appologies if I've confused the issue. Could be my memory item failure.

Ray
 
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zeke
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 9:03 am

WIederling wrote:
But that does not reflect into MTBF numbers. MTBF is an intrinsic property.


The MTBF number comes from the sensor manufacturer, obtained in their ideal test environment normally expressed in terms of hours in service. The manufacturer has the actual failure rates, cycles, hours per cycle etc. They have their own failure rates expressed in terms of per cycle, per hour etc.
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ArgentoSystems
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 10:33 am

RawSushi wrote:
ArgentoSystems wrote:
morrisond wrote:
Totally not right - the MAX would be fine without MCAS - it is stable - MCAS just keeps the controls from feeling too light at High Angle's of Attack which would make it easier for a Pilot to pull it into a stall - if they ignore the Stick Shaker, the audio warnings and the frame buffeting - making it extremely unlikely even the worst pilots in the world would put it in stall.

You make it sound like MCAS is completely redundant. You understand that that it simply impossible?


MCAS is redundant from a safety point of view. They only added it to ensure common handling characteristics between the NG and the MAX so that airlines don't have to pay for simulator time to certify pilots for the MAX.

Well then now it has became completely redundant, since the "no simulator training" thing is gone?
 
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Revelation
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 10:36 am

Virtual737 wrote:
MD80Ttail wrote:
Zero chance of this happening. The Max will fly again and be totally safe. The rest of the world won’t dare block the Max if the FAA reinstates it’s AW cert withdrawing the grounding. There will be plenty of hyperbole, chest pumping and positioning but at the end of the day will amount to nothing more than fodder for the news media.

On the face of it the MCAS issue will be solved and the plane will be safe. Period. On the backside politics if needed will come into play. Even China will pipe down if they want to keep sending their junk to the US without huge tariffs and if they want to avoid issues in the South China Sea.

Boeing is integral to our economy and national defense and rightly so.

It sounds like we've come full circle and achieved nothing then. Isn't this attitude of "we say it is good and that's all you need to know" a strong factor of why we're here in the first place? Add to that the "toe the line or we'll up the tariffs and see you near the Philippines" and it wont be long until we're here all over again.

What really scares me is that you're probably right.

I think the bold part is where you go wrong.

It's pretty clear this is going to be the most scrutinized fix ever in the history of aviation.

It's pretty clear the world's regulatory agencies are already in the loop.

The original comment was "On the backside politics if needed will come into play", not on the front side.

Would it surprise you if, once a technical solution is found, that various global politics may come in to play?

Personally, I don't see how they do not come in to play, but am hoping they are minimal.
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XRAYretired
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 11:07 am

XRAYretired wrote:
SheikhDjibouti wrote:
XRAYretired wrote:
Just to get the numbers right. The original design ran at 0.25 deg/sec, and the revised design 0.6 deg/sec. In both cases, the system was designed to abort when the AOA actual fell below the trigger value. It is in fault condition that MCAS will continue to drive AND since AOA actual may never dip below the trigger value

Ray.

I'm taking the risk that I have remembered this wrong, but regarding getting the numbers right, I'm backing planecane.
The original specification was for 0.6degrees in total.
The revised specification as seen on current MAX's, is 2.5 degrees in total, operating at 0.27deg/sec for 9.2 seconds.

(FWIW this 9.2 seconds was rounded up to "10 seconds" in FCOM Bulletin TBC-19 and EAD 2018-23-51)

However, when it comes to "there was no intention for MCAS to trim down more than 2.5degrees", I do not recall seeing this claim made anywhere else on these forums
Planecane - have you got a source?
In normal operation, why would Boeing want to limit it to a single iteration?


Appologies if I've confused the issue. Could be my memory item failure.

Ray


Yes, it was mea culpa.
www.b737.org.uk/mcas.htm
2.5 degrees in 9.26sec cycle = 0.27deg/sec. is the current design.
0.6 degrees in 9.26 sec cycle = 0.065deg/sec was the original design from reports.

So in fault condition the current design can drive full nose down in just 2 or so cycles (~25 seconds) from level flight.

Ray
 
FluidFlow
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 1:56 pm

I now read what is provided on this page: http://www.b737.org.uk/mcas.htm

The MCAS function becomes active when the AoA exceeds a threshold based on airspeed and altitude.


So there must be a table or function that determines when MCAS is needed. So if any three of this inputs is wrong due to sensor malfunction, MCAS could be triggered even if the plane is not near a stall.

Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers (for the same AoA above the activation threshold).


The stabilizer input is also dependent on the speed, therefore wrong airspeed can lead to too low or too high stabilizer input in the current situation.

The Boeing [system differences Volume 1] training manual states:
The MCAS only operates at extreme high speed pitch up conditions that are outside the normal operating envelope


This contradicts with the above mentioned functions.

The Proposed Fix:

1. To give the system input from both angle-of-attack sensors, Currently MCAS only uses data from the angle of attack sensor on the side of the active FCC, (see AoA source). The system will have split vane monitor and Mid Value Select (MVS) input. This will both enhance detection of erroneous AoA vane behaviour and the MVS signal selection will pick the average of ADIRU L & R and the previous MVS output. If the output of the two AoA vanes differ by more than 5.5 degrees MCAS will be disabled.


But if:
The MCAS function becomes active when the AoA exceeds a threshold based on airspeed and altitude.

is valid, then erroneous airspeed or altitude input will lead to MCAS activation, so while erroneous AoA input is addressed the other error source is still present.

So in my eyes Boeing designed an aircraft that has an aerodynamic behavior which is not allowed to be certified:
This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics".


Therefore they implemented a software to counteract that problem. That software can down a plane due to erroneous sensor input if pilots do not react correctly. Pilots never got trained to react correctly. To react correctly they have to use manual trim that might not work at high speeds, in which MCAS actually should be active:
The MCAS only operates at extreme high speed pitch up conditions that are outside the normal operating envelope


I hope this problems are addressed properly.
 
Elementalism
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 2:53 pm

planecane wrote:
RawSushi wrote:
planecane wrote:
I'll try to dig up the article but one of the news articles described that test pilots determined that 2.5 degrees was necessary in some cases to offset the nacelle induced lift. The way it was described indicated that 2.5 degrees would be the max needed. Also the fact that the software update will limit it to one activation per near stall event indicates that for the intended purpose only one activation and a total of 2.5 degrees is all that is necessary.


First of all 2.5 degrees regardless of airspeed sounds dangerous to me and maybe some experts can try and explain how that can even remotely be a good idea.

Secondly I think it's telling that the update limits it to one activation only. This means that using AoA to close the loop was never required in the first place and the original design was massively flawed.


It isn't 2.5 degrees regardless of airspeed. The algorithm uses AoA and airspeed to determine the nose down trim amount. The reason it went to max with the failed sensor is that the AoA was reading so nose high that if it was real the plane would stall at any speed.

100% agree with your second statement. MCAS might be the worst algorithm I've ever seen for a control system. Not just in aircraft. A cell phone charger algorithm has more intelligence.


Agreed, how MCAS was designed and deployed is shockingly terrible. I still cant fathom why they thought to only use 1 AOA input at a time. Second, why the system didnt have a limit on how much it could trim. If the plane is so nose high it requires MCAS to trim it to the max. The pilots arent doing their job or there is a severe CG issue. Either way the plane is in trouble and MCAS isnt going to fix it. But the risk is what we saw in these two plane crashes. When the system believes it is in that nose high position and trims it to the max. Resulting in a stable flying plane to nose dive at high speed.
 
xmp125a
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 4:12 pm

Elementalism wrote:
Agreed, how MCAS was designed and deployed is shockingly terrible. I still cant fathom why they thought to only use 1 AOA input at a time. Second, why the system didnt have a limit on how much it could trim. If the plane is so nose high it requires MCAS to trim it to the max. The pilots arent doing their job or there is a severe CG issue. Either way the plane is in trouble and MCAS isnt going to fix it.


Yes. But one of the design requirements was that it has to be certified as it would be essentially the same as NG and now it is obvious that there are many stupid design decisions hidden in MAX, with the sole reason, conform to the certification requirements for the same type, even if that means introducing gremlins into the plane. Sad, just sad.
 
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spinotter
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 4:55 pm

MSPNWA wrote:
RossW wrote:
A good video for the average Joe

https://youtu.be/H2tuKiiznsY


If the Average Joe wishes to be misinformed, yes, it's a good video.


I did not watch the video, but I do know that someone who states: "If the AverageJoe wishes to be misinformed" - that person has an agenda.
 
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spinotter
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 4:58 pm

xmp125a wrote:
Elementalism wrote:
Agreed, how MCAS was designed and deployed is shockingly terrible. I still cant fathom why they thought to only use 1 AOA input at a time. Second, why the system didnt have a limit on how much it could trim. If the plane is so nose high it requires MCAS to trim it to the max. The pilots arent doing their job or there is a severe CG issue. Either way the plane is in trouble and MCAS isnt going to fix it.


Yes. But one of the design requirements was that it has to be certified as it would be essentially the same as NG and now it is obvious that there are many stupid design decisions hidden in MAX, with the sole reason, conform to the certification requirements for the same type, even if that means introducing gremlins into the plane. Sad, just sad.


Very sad. I just want you to think about the inducements which allowed all of this to happen. Was it for WN's $280 million? Did the money dictate how the airplane turned out? Seems very like it to me. These were not all engineering decisions.
 
spyglass
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Re: Should airline regulators consider grounding B737 MAX series

Tue Apr 16, 2019 5:00 pm

arcticcruiser wrote:
CriticalPoint wrote:
Zaf wrote:

I have done type ratings in three different countries. One of them was in the USA. And it was by far the sloppiest. Nothing world class about it. So get off your high horse.

Oh?....details?
I remember when......a plane trip was a big deal.
 
uta999
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 5:07 pm

Could MCAS not have AGL and terrain added to its criteria? so it does not kick in at all, if so near the ground that pointing the nose down defeats any form of stall protection.

There’s little point in MCAS ‘saving’ a plane from a stall, when it’s heading into the ground or terrain.
Your computer just got better
 
L1049L1011
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 5:34 pm

FluidFlow wrote:
I have a feeling Boeing does not tell the whole truth about MCAS at what it is supposed to do. While I think its not there to prevent a stall in situations where the pilots give nose up commands in straight flight, its for situations where the plane turns probably at high speed small turning circle situations. In straight flight stick shaker and other warnings help enough.
Looking at the engine placement i have a feeling that in turns with high bank angles and high AoA the outer wing might stall way before stick shaker will activate. I also think MCAS kicks in way before stall warnings occur.
The reason i think this could be the reason for MCAS implementation is that the nacelle of the outer wing in a turn deflects the flow towards the inner part of the wing where most of the lift is normally generated. This probably happens rather sudden at a certain AoA that on the NG is no problem. Thats also why MCAS was upped from the low value of 0.6 degree to the 2.5 as the nose down has to happen fast in that situation. It must be a pretty aprupt change from a AoA needed for a sharp turn into an AoA that stalls the outer wing. The fact that test flights shown that MCAS planned to „weak“ first suggest Boeing knew in which situation it is needed from simulations and told test pilots to go into such turns to test the limits and figured MCAS needs stronger reaction to prevent a stall as it comes sudden and way before the normal stall warnings.


Thanks for the great explanation! I've wondered why MCAS might be required during steep turns:
The Maneuvering Characteristics Augmentation System (MCAS) was designed to address this, according to Boeing engineers and pilots briefed on the system, now at the center of the inquiry into the crash of Lion Air 610, a brand new Boeing 737 Max 8. MCAS is “activated without pilot input” and “commands nose down stabilizer to enhance pitch characteristics during step turns with elevated load factors and during flaps up flight at airspeeds approaching stall.”

( quote from https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/ )
 
xmp125a
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Re: B737MAX Grounded Worldwide

Tue Apr 16, 2019 5:35 pm

ArgentoSystems wrote:
RawSushi wrote:
ArgentoSystems wrote:
You make it sound like MCAS is completely redundant. You understand that that it simply impossible?


MCAS is redundant from a safety point of view. They only added it to ensure common handling characteristics between the NG and the MAX so that airlines don't have to pay for simulator time to certify pilots for the MAX.

Well then now it has became completely redundant, since the "no simulator training" thing is gone?


Is it gone? Any reliable source on this? I mean, I sincerely hope it is gone, because only that will make MAX a safe (and a very safe perhaps) plane. But I don't see it as a foregone conclusion.

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